In application Ser. No. 39,372, filed May 15, 1979, abandoned in favor of continuation application Ser. No. 239,891, filed Mar. 3, 1981, now U.S. Pat. No. 4,351,617, I describe a printer which directs a plurality of small balls about one millimeter in diameter in extremely rapid succession against a printing medium such as a ribbon overlying a sheet of paper. In the ball gun of the printer, which is movable about orthogonal axes for targeting, balls are successively introduced by an injector into a train of balls leading to a resilient breech which is slightly smaller in diameter than the balls and behind which air is maintained under pressure. The lead ball is fired by actuating the injector to feed another ball into the rear of the train to push the lead ball through the breech to the barrel side to allow the pressurized air to expand into the barrel and propel the ball outwardly.
In the ball injector, also described in my copending application Ser. No. 107,885, filed Dec. 28, 1979, now U.S. Pat. No. 4,326,644, balls to be fed fall under the influence of gravity into the spaces between the teeth of a rotary saw blade disposed at the bottom of a cylindrical ball reservoir to be carried along a circular raceway defined by the saw blade and the walls of the reservoir. At a certain point along the raceway, the balls enter a separator which redirects the balls along a straight-line ball-train path tangential to the circular raceway at the point of entry. The separator is formed with a bore corresponding to the desired straight-line path as well as with a slot for receiving the rotary saw blade. The slot is narrower than the ball diameter so that the balls are stripped from the blade teeth and injected into the bore as the blade continues to move along its circular path.
One problem experienced with the above-described ball injector involves the feeding of balls to the recesses between the teeth of the rotary saw blade. At relatively low speeds of operation below a feed rate of about 400 to 500 balls per second, the balls readily enter the recesses between the teeth. At higher speeds of operation, however, the tangential velocity of the teeth of the saw blade relative to the rate of movement of the balls along their generally downward path is such that the teeth will strike the balls as they begin to enter the recesses, deflecting them upwardly. This effect increases with speed so that, at a sufficiently high rotational velocity of the saw blade, no appreciable number of balls are able to enter the intertooth recesses.